JACKSON, Miss. — A dust mask and other items seized from the martial arts studio of a Mississippi man charged with sending poison-laced letters to President Barack Obama and two other public officials tested positive for ricin, according to a court document released on Tuesday.

Records seized by the FBI also showed that Tupelo martial arts instructor Everett Dutschke ordered castor bean seeds, used to make ricin, from eBay, FBI Special Agent Stephen Thomason said in an eight-page affidavit.

Dutschke, who is being held in jail without bond, is expected to appear in U.S. District Court in Oxford, Miss., for a detention hearing on Thursday.

Contacted by Reuters, Dutschke’s attorney, public defender George Lucas, declined to comment. In several media interviews before his arrest Dutschke maintained his innocence.

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Soon after the seeds were delivered to Dutschke’s home address, someone using his laptop computer downloaded a publication on safe handling and storage of the poison, Thomason stated.

An agent last week retrieved the contaminated dusk mask from a trash bin near Dutschke’s former tae kwon do studio. Dutschke was earlier seen by the FBI dumping items in the bin he collected from his studio, the affidavit stated.

Traces of ricin were also discovered on four items found at the studio, including liquid removed from a drain and a filter containing items vacuumed from the studio floor, the affidavit said.

When confronted with evidence by federal agents last week about his being observed disposing of items from his studio in the trash, “Dutschke attempted to change the subject, and he ended the interview,” according to the affidavit.

Dutschke, 41, was arrested at his Tupelo home on Saturday and was later charged with “developing … and possessing” ricin and “attempting” to use it “as a weapon,” according to a Department of Justice statement.

If convicted, Dutschke faces maximum possible penalties of life imprisonment and a $250,000 fine.

The ricin-laced letters, addressed to Mississippi Sen. Roger Wicker, as well as Obama, were retrieved earlier this month at off-site mail facilities before reaching their intended victims. A Mississippi state judge also received a ricin-laced letter.

Discovery of the letters fueled more national anxiety in the days after the bombing at the Boston Marathon.

Dutschke’s arrest came several days after U.S. prosecutors dropped charges in the case against another Mississippi man, Elvis impersonator Kevin Curtis, who was released from jail after a search of his home revealed no incriminating evidence.

Dutschke’s name first surfaced when Curtis’ attorney suggested in a court hearing that her client had been framed by someone, and mentioned a running feud between Dutschke and Curtis.

Suspicion had originally fallen on Curtis because of wording contained in all three ricin letters, which included his initials “KC.”

Dutschke has told local media that he knew Curtis but had only had contact with him three times, and not since 2010.

The FBI said last week more tests may be necessary to determine the potency of a granular material identified as ricin contained in the letters.

An FBI agent testified in court last week that the ricin found in the letters was in a crude form and looked like castor beans ground up in a blender, according to media accounts. Experts have said ricin in that form would have a low potency.

A material like that described in the ricin court hearing would pose little danger, according to Milton Leitenberg, senior research scholar at the Center for Strategic and International Studies at the University of Maryland.

The affidavit says Dutschke made two purchases each of 50 red castor beans from eBay in November and December of 2012 using a PayPal account.

“I understand that the number of castor beans ordered is more than sufficient to extract the quality of ricin found in the three letters,” Thomason said in the affidavit.

Among other items FBI agents collected from the trash were the box for a Black and Decker coffee grinder and a box of latex gloves.

“Based on my training, I know that a coffee bean grinder could be utilized in the process of extracting ricin from castor beans,” Thomason said in the affidavit.

The door to Dutschke’s former Tupelo Taekwondo Plus studio was padlocked after the agent found traces of ricin, the FBI said in a statement on Tuesday.

“That location was immediately sealed off and appropriate public health authorities were notified,” the statement read.

“The FBI is now conducting further forensic examination for the purpose of identifying trace evidence, residues, and signatures of production that could provide evidence to support the investigation,” it added.